He fought against simony, worked for clerical celibacy, and insisted on bishops with spotless backgrounds who could really help their flocks. He supported Otto III, but an uprising on 1 February1001 caused both pope and emperor to flee Rome for several months. When he returned it was as spiritual leader only, and he confined himself to Church matters, unusual for his day. He created ecclesiastical metropolitans for Poland and for Hungary. Crowned the king of Hungary on 27 March1000, and made him papal vicar for the country.

In addition to religious treatises, Sylvester wrote works on philosophy, mathematics and science. He is thought to have introduced the use of Arabic numerals to western Europe, and to have invented the pendulum clock. Those who knew him admired him for his learning; some common folks worried that such intelligence indicated he was in league with the devil.